Surface roughness of fine finished surfaces can be measured using the so-called total integrated scattering (TIS) method, which is based on the concept that rougher surfaces scatter more light into off-specular or non-specular directions. With this TIS method measurements of average surface roughness for an area typically 1 mm.sup.2 can be obtained.
The American Society for Testing and Materials has adopted this TIS technique as a standard test method for surface roughness. Surface profiles (e.g. two-dimensional surface scans) also can presently be obtained using stylus techniques, scanning tunnelling microscopy, scanning electron microscopy (SEM), etc. Images of surface reliefs can be obtained using optical microscopy, optical interferometry, and transmission electron microscopy, etc.
The information content of off-specularly scattered light is quite different from that of other known surface profiling and imaging techniques: TIS is characterized by the r.m.s. roughness of the surface, subject to certain wavelength limitations. All other techniques referred to above provide information of the surface shape itself.
While at least one prior art patent, Kato et al., U.S. Pat. No. 4,690,565 teaches the use of a focused light beam to scan certain features on a surface under examination as well as monitoring the scattered light by collimating it through the use of a parabolic or spherical mirror and detect the output with photo sensors, this invention only collects a small fraction of the scattered light.
As a consequence, when only a fixed solid angle of the scattered light is collected as taught by Kato et al., the method becomes inherently insensitive to certain types of surface features and no quantitative results can be obtained. In addition, the Kato et al. patent does not make any provision for removing the specularly-reflected laser light beam which can subsequently be scattered by the focusing lens since it is then traveling in the opposite direction.
As a result of the deficiencies of the known prior art patents, there has existed a long standing need among those individuals involved in this area of technology for a scanning scattering microscope arrangement having a high sensitivity for detecting roughness; and, wherein the techniques employed produce quantitative results sensitive to a broad range of surface features. The provision of such a device being a stated objective of the present invention.